A Symphony in Bullfrog Major

For four years, I studied the science of biodiversity and ecology – in the classroom. Yes, we did experience the occasional field trip (including a “fermentation” class at South African Breweries), but although we enjoyed a few rare moments immersed in nature, I cannot recall ever witnessing a frog “croaking”. Admittedly, I am a squeamish sort of girl (much to my father’s disappointment), so perhaps this was the real reason for my lack of observation. Whatever the case, nothing could have fully prepared me for the mighty call of Southern Africa’s largest amphibian: Pyxicephalus adspersus, or simply, the African Bullfrog.

Bullfrogs spend most of their days buried underground. In fact, certain areas of their range can be completely dry for years at a time and reach surface temperatures of over 38oC! During this period, the frogs protect themselves inside an underground estivation chamber. This is created by shedding several layers of the skin’s epidermal cells, forming a tough cocoon that prevents the evaporation of body fluid. Once dormant, the frog’s bodily functions will slow or shut down all together, only absorbing the water stored in the bladder. This process is so successful that they can remain underground for over a year, only emerging after heavy rainfall. A single downpour of more than 60mm will awaken these large amphibians from their slumber and create shallow, temporary water bodies perfect for breeding. Thus the Bullfrog symphony begins.

Peekaboo, I see you!

Like birds, it is only the male frogs that call. These calls advertise their species, general fitness, size, territory and location to other males and females. This acoustic communication strategy is beneficial in that it helps the concealed amphibians locate one another while evading predators. In frogs and toads, sound is produced when the nostrils are closed and air from the lungs is pushed over the vocal chords and through the wind pipe into the air sac (that skin sack below the chin that prods out to the front). This air sac acts like a resonance chamber, which magnifies the sound. In the case of the breeding bullfrog, the call produced is a soft, deep “whooooop”.

While most male frogs use their calls to ward off other males, bullfrogs have a slightly more aggressive approach. Larger males occupy the centre of the temporary “breeding arenas” and will attack other males that enter their territory, often causing injury or killing one another. Most females will typically mate with the most dominant bull within the territory.

A dominant male Bullfrog mates will a female near the centre of the water body

After mating, the largest male bullfrogs will remain at the breeding site to look after the offspring. And they are exceptional fathers. Parenting male bullfrogs will physically attack animals or people that threaten their offspring, and will use their back legs to dig channels at the periphery of the breeding site to improve environmental conditions for the growth and survival of their eggs or tadpoles.

After a prolonged dry spell, Welgevonden finally received an abundance of rain over the Festive Period. This has prompted a flurry of bullfrog activity in the shallows of many of the newly formed water bodies scattered across the reserve. Be sure to request to observe these curious creatures while out on game drive. I can vouch that even the most squeamish of visitors will find these frogs fascinating, but be sure to keep a good distance from the water to be safe!

-Jess Oosthuyse

Fact Sheet

Name (Scientific) Pyxicephalus adspersus
Name (English) African Bullfrog
Name (French) Grenouille taureau d’Afrique australe
Name (German) Afrikanischer Ochsenfrosch
Name (Spanish) Pyxicephalus adspersus